Initial commit

Infra/Encoders/Crc32.cs

@@ -0,0 +1,33 @@
+namespace StitchATon2.Infra.Encoders;
+
+public static class Crc32
+{
+    private static readonly Lazy<uint[]> LazyTable = new(GenerateTable);
+    private static uint[] Table => LazyTable.Value;
+
+    public static uint Compute(Span<byte> buffer, uint initial = 0xFFFFFFFF)
+    {
+        uint crc = initial;
+        foreach (var b in buffer)
+        {
+            crc = Table[(crc ^ b) & 0xFF] ^ (crc >> 8);
+        }
+        return ~crc;
+    }
+
+    private static uint[] GenerateTable()
+    {
+        const uint poly = 0xEDB88320;
+        var table = new uint[256];
+        for (uint i = 0; i < 256; i++)
+        {
+            uint c = i;
+            for (int j = 0; j < 8; j++)
+            {
+                c = (c & 1) != 0 ? (poly ^ (c >> 1)) : (c >> 1);
+            }
+            table[i] = c;
+        }
+        return table;
+    }
+}